There are many entry points to teaching about the life cycle of a star. You may want to tackle star life cycles during your unit on the solar system. After all, our Sun is an average yellow dwarf star, and students will be curious about how long it will burn to support life on Earth. You may want to teach about the life cycle of a star while you are explaining the origins of the universe. You could even incorporate chemistry and explain where all those elements on the periodic table come from. Spoiler alert: they come from stars. Whenever you decide to teach your students about stars, you will want to focus on the vocabulary of stars and the story of a star.
Stories are a powerful tool in science. Our brains are hardwired to pay attention to stories, and when our students are paying attention, they are learning.
Start with Questions
We also want our students to be curious and ask questions. However, sometimes, a topic is so new to students that they don’t even know what to ask. Providing them with starting questions will help them engage with the material. They can generate more questions as they learn.
Here are some questions to get your students thinking about the life cycle of a star:
- Where do stars come from?
- Do stars last forever?
- What happens to stars?
- Where is the Sun in the life cycle of a star?
- How do scientists know about the life cycle of a star?
- Why are stars different sizes?
The Story of the Life Cycle of a Star
The story of a star starts with a nebula. A nebula is a giant cloud of gas, ice, and dust. Eventually, gravity brings the matter in the nebula together to form a protostar.
A star forms when the pressure at the protostar’s core reaches 15,000 degrees Celsius and nuclear fusion starts. During nuclear fusion, four hydrogen atoms fuse to form a helium atom. A helium atom has slightly less mass than four hydrogen atoms. The difference in the masses is released as energy. Albert Einstein’s famous equation, E = mc2, showed how matter could be converted into energy. The c in the equation represents the speed of light, which is 186,282 miles per second – a huge number! It doesn’t take much mass to make a lot of energy.
The amount of energy a star makes, and its resulting brightness, depends on how much matter was in the nebula that formed the star. Large stars are brighter than smaller stars. The life cycle of a star depends on its mass. Smaller stars are dimmer, but they also burn for longer than larger stars. A large, bright star can burn for just a million years, while a dimmer star can burn for billions of years. The Sun is an average star with a life expectancy of about 10 billion years. We are nearly halfway through the Sun’s life.
Main Sequence Stars
When a star has nuclear fusion creating hydrogen at its core, we call it a main sequence star. In a main sequence star, the pressure of the energy being generated in its core is equal to the pull of gravity, so the star stays the same size. However, when the star runs out of hydrogen atoms, the pressure of gravity is unbalanced, and the core collapses in on itself, becoming even hotter. The outer layers of the star expand away from the hot core and then cool. At this point in the life cycle of a star, the low-mass stars become red giants, and high-mass stars become red supergiants. A high-mass star has about ten times the mass of our Sun.
Giants and Supergiants
Inside the incredibly hot cores of giants and supergiants, helium atoms fuse to form carbon atoms and energy. When the star has used up all of its helium, the core will again condense and get hotter while the outer layers expand again.
In red giants, the outer layers are pushed so far away from the super-dense core that they escape into space. All that is left is a tiny, dense core about the size of Earth called a white dwarf. Gravity pulls the atoms of the white dwarf together until only the force of electrons repelling each other keeps the star from collapsing in on itself. After about four billion years, the white dwarf will have cooled and become a black dwarf.
Things get crazier for red supergiants. As a supergiant runs out of fuel, its core collapses similarly to a red giant. However, a red supergiant is so massive that it can create helium, carbon, oxygen, neon, silicon, and iron through nuclear fusion. Iron is so stable that it will not undergo nuclear fusion in the star’s core.
When the star has a core full of iron, the pull of gravity is so strong that it collapses the star in one second. Temperatures in the core reach 100 billion degrees Celsius. The repulsive forces of the atoms within the core are stronger than gravity, so they explode out. This explosion superheats the other layers of the star so much that even heavier atoms and radioactive isotopes are created from nuclear fusion. The shockwave of the exploding star sends these heavy atoms into space. We call an exploding red supergiant a supernova.
In smaller high mass stars, the core left over after a supernova is called a neutron star because the only thing left in it are neutrons. A neutron star is so dense that just a teaspoon of it would weigh 100 million tons on Earth.
In larger high mass stars, the core left over after a supernova is so dense that nothing can stop the pull of gravity, and the star’s core collapses to the point that it has no volume. It has so much gravity that not even light can escape. We call this a black hole. While the gravity inside a black hole is extreme, it does not pull matter into itself. It acts like any other massive object in space. In fact, planets, stars, and even galaxies can orbit around black holes.
The story of the life cycle of a star is a long, beautiful story full of scientific principles and mysteries.
If you want your students to learn about stars, you will need them to first pay attention to the story, and then you will need them to remember the story. Here are some ideas on how to do that.
How to Get Your Students to Pay Attention to the Life Cycle of a Star
First, let your students chose how they learn about the life cycle of stars. Some students may choose to read about it, but others may feel more comfortable watching a video. Still, others may want to hear it from you, so they can ask questions as they learn. By providing your students with options for how they learn, you empower them to take control of their learning and allow them to enjoy it.
You will want to make sure that all students are responsible for the same basic information no matter how they learn. You could give students a questions page, similar to mine, to help keep them focused. While you can create your own or purchase the one I created. For just $2, you will save valuable time. I have also gathered my favorite videos on the life cycle of the Sun. You can check them out below.
Next, you will want your students to do something with the information they learn. Answering questions is always a good option, but this is a perfect opportunity to get creative. You students can write a song describing the life cycle of a star. They can create a skit, a picture, or a diagram. You can also keep it simple. Have students show you their notes or work in small groups to create a mind map of what they learned. No matter what you choose, having students work with the material in a meaningful way will communicate to their brains that the information is important and worth remembering.
Help Your Students Remember What They Learn
Finally, you will want to give your students plenty of opportunities to remember what they learned. My favorite tool for repeated practice is flashcards. Flashcards are easy to make, can be taken anywhere, and only require a few minutes of practice a day. Plus, they are incredibly effective at helping us remember. Want to use flashcards but also want to save time? I have you covered. You can grab my life cycle of a star flashcards here.
You can also incorporate review questions into daily quizzes, have students write questions about the material, or integrate the life cycle of a star into your later lessons. However you chose to do it, you will want to give your students at least five opportunities to practice remembering what they learned between learning about the life cycle of a star and taking a test on the material.
ARE YOU TEACHING ANOTHER SCIENCE TOPIC?
I am working on creating more science units so that every science teacher can get exactly what he or she needs for her students. You can also read about how I use brain science to teach other science topics on my blog. Click the pictures below to learn more.